Pulse-echo radio locator system



Oct. 3, 1950 MESNER 2,524,295

PULSE-ECHO RADIO LOCATOR SYSTEM Filed Sept. 24, 1945 IN V EN TOR.

Ma net BY 2 I Patented Oct. 3, 1950 PULSE-ECHO RADIO LOCATOR SYSTEM Max H. Mesner, Princeton, N. J assignor to Radio Corporation of America, a. corporation of Delaware Application September 24, 1945, Serial No. 618,341

2 Claims. (01. 34311) My invention relates to radar systems and particularly to radio locator systems such as those of the type known as the plan-position-indicator (P. P. I.) systems.

An object of the invention is to provide a method of and means for obtaining improved radio locator indications.

A further object of the invention isto provide a method of and means for improving the signalto-noise ratio in a radio locator system.

A still further object of the invention is to provide an improved radar system of the type giving both distance and angular position information.

The invention will be described as applied to a P. P. I. system wherein radio pulses are radiated from a directive antenna while it is being rotated to scan a certain area. In the case illustrated, the antenna is rotated through 360. The P. P. I. picture appears on the screen of a cathode ray tube that has a rotatable deflecting yoke. The deflecting yoke is rotated in synchronism with the directive antenna and, at the same time, a sawtooth deflecting current is supplied to the yoke for deflecting the cathode ray of the indicator tube radially in synchronism with the radio pulse transmission.

According to the present invention, the abovementioned radial deflection is produced after a plurality of radio pulses have been radiated from the antenna and after the resulting reflected pulses picked up by the antenna have been stored on the storage screen of a cathode ray storage tube. The stored pulses are taken off the storage screen during and in synchronism with the radial deflection of the indicator tube beam. The pulses thus taken 011" are applied to a control electrode of said indicator tube. Since noise signals occur at random intervals whereas the radio pulses occur at regular intervals, an improvement in the signal-to-noise ratio may be obtained in this way.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which the single figure is a block and circuit diagram of one embodiment of the invention.

Referring to the drawing, there is shown a radar system comprising a radar station of the pulse-echo type. The radar station comprises a radio transmitter III which is pulse modulated by electrical pulses supplied from a pulse generator II. The radio pulses from transmitter it are supplied through an antenna duplexer unit, such as the T-R box l2, to a directive antenna l3. The T-R box may be of the type described in application Serial No. 488,959, flied April 21, 1943.

in the name of Thomas L. Gottier and entitled Antenna Duplexing. Reflected pulses are picked up by the antenna i3 and supplied through the T-R box l2 to a radio pulse receiver H where they are amplified and demodulated. The resulting video-frequency pulses, indicated in the graph l5 as-reflected pulses, are supplied over aconductor ii to a control electrode l'l in the put-on section l8a of a storage tube l8. =The'electron beam of the put-on section is deflected trans versely across the storage element strips 28 of a storage screen 29 in synchronism with the modulating pulses produced by the pulse generator II.

This deflection of the put-on beam is produced by sawtooth voltage waves, shown by the graph 20, which are supplied from a sawtooth generator 3| to a pair of deflecting plates 32. a

The particular storage tube that is illustrated I is the same as that described in application Serial No. 492,658, filed June 26, 1943," in the names of Harley Iams, Albert Rose and Gardiner L. Krieger and entitled Cathode Ray Storage Tube, now Patent No. 2,454,652, issued November 23, 1948.

The reflected pulseswhich have been stored on the storage element strips 28 by the put-on beam are taken off the storage screen 29 by thetake-ofl cathode ray or beam which is produced in a takeoif section lb. The take-on" beam' is deflected transversely across the storage strips 28 by means r of a pair of deflecting coils 33 which are supplied with sawtooth current from a rotating potentiometer arm that makes sliding contact with a potentiometer resistor 36. This deflection of the take-off beam'is in synchronism with the deflection ot the cathode ray of a cathode-rayindicator tube 31.

The signal pulses taken oil the storage screen" mechanical coupling between the motor and the v yoke 5| and antenna I3 being indicated by the broken lines.

The potentiometer arm 34 is also rotated in a fixed time relation to the antenna rotation by means of a connection through gears indicated at '53. -A battery 54 produces a flow of current through the resistor winding 36 so that a sawtooth.

voltage wave, illustrated at 56, is produced at the arm M as it slides along the resistor winding. In the example shown, the resistor winding 36 is wound on a portion of an insulating supporting ring 40.

In the present example, the potentiometer arm 34 is rotated 36 times per single rotation of the antenna l3. Thus, by applying the deflectingv wave 56 to the deflecting yoke ii, the cathode ray of the tube 36 is deflected radially 36 times during one rotation of the yoke It will be noted that it is during each of these radial deflections that the take-off beam sweeps across the storage screen 29 thereby causing the stored pulses to be applied to the control grid 13.

Since the reflected pulses are taken oi! the storage screen 29 in synchronism with the radial deflection at the tube 31, the spots 50 appearing on the radial traces on the indicator tube screen 49 are at distances from the center of the screen which correspond to the distances of the reflecting objects from the radar station. It will be apparent that each pulse taken oif a storage element 28 by the take-oil beam is a charge that has been built up by a plurality of the pulses reflected from an object. This is assuming that the said reflecting object is stationary or is not moving too rapidly whereby said plurality of pulses causes the put-on beam to build up the charges on the same storage element or elements of the screen 29. Noise signals, on the other hand, occur at random intervals and the stored charges produced by them will be distributed over the various storage elements 28 so that no large charge will be built up by the noise signals at any one point on the storage screen. As a result, an improvement in the signal-to-noise ratio is obtained.

The construction of the storage tube 3 will be described generally, no detailed description being necessary as the present invention does not cover the storage tube per se.

The put-on section l8a includes a cathode 6|, the control electrode H, a first anode 62, a second anode 63, and a collector electrode 64. Suitable voltages are applied to produce a high velocity put-on beam.

The take-off section I8b includes a cathode 68, a control electrode 61 held at a fixed bias potential. a screen grid 68, a first anode 69, and a second anode H. Two ring or frame-like electrodes 12 and I3 are positioned between the second anode H and the screen 29 for slowing down the electrons of the beam after they leave the region of the second anode. Thus a low velocity take-off beam is obtained at the screen 29.

The storage screen 29 may comprise a supporting sheet of mica 16 which has the conducting strips 28 on the beam side and a metal coating 11 on the opposite side. In the example shown, the coating 11 is used as a signal plate for taking on the stored signals. It should be understood that the invention is not limited to the specific type of storage tube illustrated.

I claim as my invention:

1. A radar system comprising means for transmitting periodically recurring pulses of radio energy in the form of a directional radio beam, means for scanning a region by said beam, means for receiving said pulses after reflection from objects in said region, a cathode ray storage tube having a storage screen and including means for producing at least one cathode ray beam and directing it against said screen, means for defleeting a beam of said storage tube across said screen in synchronism with the transmission of said pulses, means for modulating said beam during said deflection by said received pulses whereby they are stored on said screen, a cathode ray indicator tube which includes a phosphorescent screen and means for producing a cathode ray that is directed toward said phosphorescent screen, means for producing a deflecting field ior deflecting the cathode ray of the indicator tube radially, means for rotating said deflecting field in synchronism with said radio beam scanning, means for periodically taking signal on said storage screen only after a plurality of said flrstmentioned deflections have occurred whereby the take-off repetition rate is substantially less than the repetition rate of said transmitted pulses, means for radially deflecting-the cathoderay of said indicator tube in synchronism with said signal take-on, and means for supplying to an output lead the stored pulses taken ofl the storage screen by the beam during said signal take-oil, and means for modulating the cathode ray of said indicator tube by the signal appearing in said output lead.

2. A radar system comprising means for transmitting periodically recurring pulses of radio energy in the form of a directional radio beam, means for scanning a region by said beam, means for receiving said pulses after reflection from objects in said region, a cathode ray storage tube having a storage screen and including means for producing a cathode ray put-on beam and a cathode ray take-on beam, means for deflecting said put-on beam across said screen in synchronism with the transmission of said pulses, means for modulating said put-on beam by said received pulses whereby they are stored on said screen, a cathode ray indicator tube which includes a phosphorescent screen and means for producing a cathode ray that is directed toward said phosphorescent screen, means for producing a deflecting field for deflecting the cathode ray of the indicator tube radially, means for rotating said deflecting field in synchronism with said radio beam scanning, means for deflecting the take-oil beam of said storage tube across said storage screen only after a plurality of deflections of said put-on beam have occurred whereby the repetition rate is substantially less than the repetition rate of said transmitted pulses, means for radially deflecting the cathode ray of said indicator tube in synchronism with the deflection of said takeoff beam, and means for supplying to an output lead the stored pulses taken off the storage screen by the take-oil beam during its deflection, and means for modulating the cathode ray of said indicator tube by the signal appearing in said output lead.

MA! H. MESNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,403,562 Smith July 9, 1946 2,412,669 Bedford Dec. 17, 1946 2,430,038 Wertz Nov. 4, 1947 

